Thank you! That's very helpful!

It's odd because looking at the map, we really should be in zone 7b. And the only reason I can think that maybe we're not is because we're in an inlet of the lake. Does that make a difference?

Lakes (and oceans) are large thermal reservoirs that prevent large temperature fluctuations. If really cold air is flowing in, having a warm lake nearby helps. The USDA zone is explicitly about how cold it gets in the winter. If you look at a USDA zone map, it's easy to see that the coldest places in the winter are places farthest away from the water.

I'd go for seedlings. Brassicas do well over the winter in the Carolinas. I tried growing sprouting broccoli and broccoli in the winter in NC. They did ok in containers, but I think they would do a lot better planted in the ground!

Garlic I'm in 8a and just planted some elephant garlic.

if you have a more specific location (and microclimate details) that would help. But generally, but 8a in SC is generally more than plenty warm enough to start seeds in ground. If you have a thermometer measure of the soil, that will tell you. The ground just needs to maintain 60 for a week for most germination. And I'm sure you'll have that. You could start inside as well. Most brassicas (kale, broc, brussel sprouts, cabbage) as folks have mentioned. Garlic and their cousin - the leek is a favorite. Radish, carrots do well. If you throw up a frost cloth or plastic on a frame, you'll be fine with more fragiles like spinachy in milder freezes. I'm in VA and Kale, leeks, garlic, radish, carrots all make it through winter. If no hard freezes, all the listed brassicas make it.

The plot I've been given still has a few pepper plants from its previous tenant. There's a few pepper trying to grow on them. Should I throw some plastic over them and see what I can get out them? Or give them up and turn them into compost?

Peppers are notoriously frost intolerant, and they grow poorly in cool temperatures. It's going to be hard to convince them to stay alive and kicking over a 8a/7b winter. Might as well keep them going until a frost takes them out.

While I agree that the ground is warm enough to start seeds there, just-germinated seedlings are pretty fragile, and low temperatures don't suit them that well. Unless you are putting in loads of small plants (radishes, carrots, beets, etc.) you might be better off growing seedlings in controlled conditions, and set them out when they are larger.

there isn't enough strong sunlight this time of year to get a lot of growth on most things. It's best to start your fall or winter garden plants in late summer and just maintain them over the winter. Most of them can handle frosts (some even improve in flavor) but they don't grow much. If you can cover them with plastic you can get some happy winter greens but you'll have to manage them every day and throughout the day - uncover if it gets hot, cover again each night.

Well, that depends on where you are. If you are sufficiently south, winter is not all that sun-free, and for many plants, which simply can't stand intense summer heat, that's the right time to grow them. Many of my summer plants do well with five hours of high sun, and winter plants, if in an area where the sun isn't blocked, won't get much less sunlight than that. My brassicas, beets, and carrots grow fine in the winter here. I can't even try growing those things in the summer.

lettuce,garlic, and spinach